Container for molten metal

ABSTRACT

A container for molten metal includes an outlet for outflow of the molten metal from the container and a temperature measuring device fixed in a wall of the container. The temperature measuring device includes a plug, an outer protective sheath having a closed end, and an inner protective tube having a closed end. The inner protective tube is arranged within the outer protective sheath. A thermocouple is arranged within the inner protective tube. The plug includes a substantially refractory material and the outer protective sheath consists essentially of substantially refractory metal oxide and graphite. The outer protective sheath extends away from the first end of the plug and projects into a recessed portion of the wall of the container. The closed end of the outer protective sheath is arranged in the recessed portion. A junction of the thermocouple is proximate to the closed end of the inner protective tube.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/706,998, filed Feb. 17, 2010, which claims the benefit of U.S.Provisional Patent Application Nos. 61/153,480, filed Feb. 18, 2009, and61/176,316, filed May 7, 2009, the entire contents of which areincorporated by reference herein.

BACKGROUND OF THE INVENTION

The invention relates to a device for measuring the temperature of metalmelts and, more particularly, for continuously measuring the temperatureof a molten metal through the wall of a metallurgical container orvessel. The invention further relates to the use of porous purging plugsin such containers or vessels.

Porous purging plugs have a key role when manufacturing steel. One ormore porous purging plugs are replaceably mounted in the bottom of aladle or other metallurgical vessel. In the vessel, varioushigh-temperature chemical processes are carried out in which the porouspurging plug is crucial, since inert gas, such as argon, is conveyedthrough the plug for purging the molten metal. Generally, bubbles arecreated by the purge gas, which cause a vortex of steel around the plug,leading to a buildup of metal on the plug. Chemical erosion of the plugis caused by metal build-up and physical erosion is caused by continuouswashing of the steel against the plug. Thus, the uppermost portion ofthe purge plug is typically heavily worn during the metallurgicalprocess. Accordingly, the purge plug has to be replaced regularly by anew purge plug when its height has shrunk to a minimum permissiblelevel. Conventional purge plugs, as such, are not highly reliablecomponents for vessels used in manufacturing steel.

It is also generally known from the prior art to use or arrange athermocouple device in a wall of a metallurgical vessel. In conventionalarrangements, the thermocouple device may be susceptible to chemical andmechanical damage due to the molten metal environment in which it isused. Also, it may take a relatively long period of time for thethermocouple device to reach its equilibrium temperature with the metalmelt, so that measurements of the melt cannot be taken quickly andefficiently.

BRIEF SUMMARY OF THE INVENTION

Therefore, it would be desirable to provide a temperature measuringdevice for molten metals that is more durable and functional. Applicanthas discovered that a device which provides a porous purge plug inconjunction with a temperature measuring element would be particularlydesirable, since the gas injected from the purge plug could serve as anadded means of protection for the temperature measuring element.Applicant has further discovered that a temperature measuring devicewhich is arranged in a recessed portion of a metallurgical vessel wouldbe particularly desirable, as metal which has solidified in the recessedportion may protect the temperature measuring device against mechanicaland chemical damage.

Briefly stated, the present invention is directed to a temperaturemeasuring device for molten metal which includes a porous plug having afirst end and an opposed second end, an outer protective sheath having aclosed end, an inner protective tube having a closed end, and athermocouple arranged within an interior of the inner protective tube.The outer protective sheath extends away from the first end of theporous plug and the inner protective tube is arranged within an interiorof the outer protective sheath. The porous plug comprises asubstantially refractory material and the outer protective sheathconsists essentially of substantially refractory metal oxide andgraphite. A junction of the thermocouple is proximate to the closed endof the inner protective tube.

In another aspect, the present invention is directed to a container formolten metal including an outlet for outflow of the molten metal fromthe container and a temperature measuring device fixed in a wall of thecontainer. The temperature measuring device includes a plug fixed in awall of the container, an outer protective sheath having a closed end,an inner protective tube having a closed end, and a thermocouplearranged within an interior of the inner protective tube. The plug has afirst end and an opposed second end and the inner protective tube isarranged within an interior of the outer protective sheath. The plugcomprises a substantially refractory material and the outer protectivesheath consists essentially of substantially refractory metal oxide andgraphite. The outer protective sheath extends away from the first end ofthe plug and projects into a recessed portion of the wall of thecontainer. The closed end of the outer protective sheath is arranged inthe recessed portion. A junction of the thermocouple is proximate to theclosed end of the inner protective tube.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe invention, will be better understood when read in conjunction withthe appended drawings. For the purpose of illustrating the invention,there are shown in the drawings embodiments which are presentlypreferred. It should be understood, however, that the invention is notlimited to the precise arrangements and instrumentalities shown. In thedrawings:

FIG. 1 is a schematic, side cross-sectional view of a container formolten metal having a temperature measuring device, according to anembodiment of the invention, arranged in the bottom wall of thecontainer;

FIG. 2 is a schematic, perspective view of a temperature measuringdevice according to one embodiment of the invention;

FIG. 3 is a schematic, longitudinal cross-sectional view of thetemperature measuring device according to the embodiment of FIG. 2;

FIG. 4 is another longitudinal cross-sectional view of the temperaturemeasuring device according to the embodiment of FIG. 2, showing thethermocouple inserted therein;

FIG. 5 is a schematic, side cross-sectional view of a portion of a wallof the container for molten metal having a recess for the temperaturemeasuring device according to another embodiment of the invention;

FIG. 6 is partial cross-sectional view of a temperature measuring deviceaccording to a further embodiment of the invention;

FIG. 6A is an enlarged cross sectional view of the circled portion A ofthe temperature measuring device shown in FIG. 6;

FIG. 7 is partial cross-sectional view of a temperature measuringdevice, according to a still further embodiment of the invention; and

FIG. 7A is an enlarged cross sectional view of the circled portion A ofthe temperature measuring device shown in FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1-5, a temperature measuring device 10 is shown forcontinuously measuring the temperature of molten metal. In oneembodiment shown in FIG. 1, the temperature measuring device 10 is fixedin a metallurgical vessel 12 through a bottom wall thereof. Themetallurgical vessel 12 may be any appropriate container for moltenmetal that is typically used in connection with steelmaking processesfor transporting molten metal to melting, refining, ladle metallurgy,and teeming operations. Preferably, the metallurgical vessel 12 is aladle having a bottom wall 14 and a generally tubular sidewall 16. Thetubular sidewall 16 extends upwardly away from and surrounds the bottomwall 14. The metallurgical vessel 12 also includes an outlet 13 foroutflow and removal of the molten metal from the vessel 12. Preferably,the outlet 13 is formed in the bottom wall 14 of the vessel 12 and isprovided with a mechanism for controlling the outflow of the moltenmetal, such as a stopper rod (not shown) or a sliding gate (not shown).

Referring to FIGS. 1 and 5, the metallurgical vessel 12 preferablycomprises a refractory material. Specifically, the metallurgical vessel12 may comprise a metal shell 18 with a refractory material lining 20interior of the metal shell 18. Preferably, the refractory lining 20comprises a refractory brick material. However, it will be understood bythose skilled in the art that any refractory material capable ofproviding sufficient resistance against molten metal penetration,corrosion resistance and thermal spalling resistance may be used. Thetemperature measuring device 10 may be secured through a wall of themetallurgical vessel 12 with fireproof mortar, and may be held in placeby a metal cover (not shown) that is bolted or otherwise secured to anexterior surface of the metal shell 18 of the vessel 12.

The temperature measuring device 10 of the present invention ispreferably fixed in either the bottom wall 14 or the sidewall 16 of thevessel 12. Referring to FIGS. 2-4, the temperature measuring device 10comprises a plug 22, an outer protective sheath 24 having a closed end24 a, an inner protective tube 26 having a closed end 26 a, and athermocouple 28 arranged within an interior of the inner protective tube26. A hot junction 29 of the thermocouple 28 is proximate to the closedend 26 a of the inner protective tube 26, as shown in FIG. 4.

Referring to FIG. 3, the plug 22 preferably has a first end 22 a, anopposed second end 22 b and a tapered porous body 23 formedtherebetween. Specifically, the body 23 of the plug 22 tapers or narrowsfrom the second end 22 b toward the first end 22 a, and is generallyshaped as a truncated cone having its smaller, truncated end pointingtoward the interior of the metallurgical vessel 12 in the installedstate. The porous body 23 of the plug 22 comprises a substantiallyrefractory material and is fitted in an opening in the bottom wall 14 orsidewall 16 of the vessel 12, as shown in FIGS. 1 and 5. Preferably, therefractory material of the plug 22 comprises one or more of thematerials alumina, magnesia, and a castable alumina-spinel castable,particularly a magnesia-alumina spinel. However, it will be understoodby those skilled in the art that the plug 22 may be made of anyappropriate refractory material having a sufficiently high thermalstrength and providing sufficient resistance against molten metalpenetration, corrosion resistance and thermal spalling resistance.Further, the body 23 of the plug 22 is assembled on or at leastpartially encased by a metal housing 30. Preferably, the housing 30comprises steel or iron. Due to the refractory material of the plug 22,any portion of the body 23 of the plug 22 that is directly exposed tothe molten metal has a non-stick surface which is highly resistant toerosion and to adherence by the slag and molten metal.

Referring to FIGS. 3-4, the outer protective sheath 24 is secured withina straight cylindrical recess 46 formed in the first end 22 a of theplug 22. A length of the outer protective sheath 24 extends upwardlyaway from the first end 22 a of the plug 22, such that the closed end 24a of the outer protective sheath 24 is a distal end. The portion of theouter protective sheath 24 which is secured within the plug 22 has agenerally straight cylindrical shape, while a majority of the portion ofthe outer protective sheath 24 extending away from the plug 22 has agenerally tapered cylindrical shape. Specifically, the body of the outerprotective sheath 24 tapers or narrows from a position proximate to thefirst end 22 a of the plug 22 toward the closed end 24 a, such that theclosed end 24 a is a tapered end pointing toward or extending into theinterior of the metallurgical vessel 12 in the installed state.

The inner protective tube 26 is arranged within an interior of the outerprotective sheath 24, such that the inner protective tube 26 alsoextends upwardly away from the first end 22 a of the plug 22 and towardthe closed end 24 a of the outer protective sheath 24. The innerprotective tube 26 is preferably a single or monolithic alumina tube.The inner protective tube 26 may alternatively be in the form of adouble tube or as a plurality of individual tube segments.

The outer protective sheath 24 is a thermally conductive refractory bodyformed essentially of substantially refractory metal oxide and graphite,such that the outer protective sheath 24 is sufficiently resistant toaggressive molten metal, particularly molten steel, and is suitable forlong-term use. More preferably, the outer protective sheath 24 consistsessentially of aluminum oxide and graphite, wherein aluminum oxidecomprises approximately 20 to approximately 80 wt. % of the refractorymaterial and graphite comprises approximately 5 to approximately 60 wt.% of the refractory material. It will be understood by those skilled inthe art that the outer protective sheath 24 may also contain carbon in aform other than graphite and/or may contain other appropriate refractoryoxides.

With the inner protective tube 26 being arranged in the outer protectivesheath 24, an intermediate space 34 is formed therebetween, and aninsulating material and an oxygen-reducing material may be arranged inthe intermediate space 34. The insulating material preferably comprisesan oxide, such as aluminum oxide, and the oxygen-reducing materialpreferably comprises a base metal, such as aluminum.

Referring to FIGS. 6 and 7, the insulating material and theoxygen-reducing material may be in the form of either a powder mixtureor in the form of a compacted tube 37 formed from the powder mixture.According to the latter embodiment, the powder mixture tube 37 surroundsthe inner protective tube 26 with a first spacing 36, as shown in FIGS.6A and 7A. Alternatively, or additionally, the powder mixture tube maybe surrounded by the outer protective sheath 24 with a second spacing38, as shown in FIG. 6A. According to another embodiment, shown in FIG.7-7A, an entire outer surface of the powder mixture tube 37 engagessubstantially an entire inner surface of the outer protective sheath 24.Because the powder mixture tube 37 is movable relative to either or bothof the inner protective tube 26 and the outer protective sheath 24, theoverall configuration of the temperature measuring device 10 compensatesfor thermal stresses and the temperature measuring device 10 is lesssusceptible to breakage. It will be understood by those skilled in theart that any appropriate configuration of the insulating material andoxygen-reducing material may be used, such as the oxygen-reducingmaterial being in the form of rods, wires, pellets or granules embeddedin the insulating material, which is a fill material.

As described above, the body 23 of the plug 22 is arranged or fixed inthe bottom wall 14 or sidewall 16 of the vessel 12. Referring to FIG. 5,according to a preferred embodiment of the present invention, the bottomwall 14 or sidewall 16 includes a recessed portion 40 where thetemperature measuring device 10 is arranged. Preferably, the recessedportion 40 is formed in the bottom wall 14 of the vessel 12.Specifically, the recessed portion 40 is formed in the refractory lining20 of the vessel 12.

According to this embodiment, with the plug 22 fixed in a wall of thevessel 14, the body 23 of the plug 22 is fixed in the refractory lining20, while the outer protective sheath 24 of the temperature measuringdevice 10 extends into the open area 40 a of the recessed portion 40. Assuch, the sensing portion 44 of the device 10, comprising the hotjunction 29 of the thermocouple 28, the closed end 26 a of the innerprotective tube 26 and the closed end 24 a of the outer protectivesheath 24, is positioned within the open area 40 a and surrounded by thewalls 42 of the recessed portion 40.

During use and operation of the metallurgical vessel 12, the moltenmetal contained in the vessel 12 can freely flow into the recessedportion 40 of the vessel 12, thereby surrounding the sensing portion 44of the temperature measuring device 10. The thermocouple 28 remainsprotected from the harsh erosive mechanical and chemical conditions ofthe molten metal environment by the insulating material, theoxygen-reducing material, the inner protective tube 26 and the outerprotective sheath 24. Also, with the sensing portion 44 extending intothe recessed portion 40, the sensing portion 44 remains in thermalequilibrium with the molten metal contained within the vessel 12. Also,after operation of the vessel 12 has ceased, the molten metal which hasflowed into the open area 40 a of the recessed portion 40 solidifiestherein. Accordingly, when the vessel 12 is drained, the solidifiedmetal remains in the recessed portion 40, surrounding the sensingportion 44 of the device 10, even after the vessel 12 is completelydrained. The solidified metal will protect the sensing portion 44 and,particularly the thermocouple 28, from mechanical and chemical damageuntil the vessel 12 is refilled with the next charge of molten metal.

According to a further embodiment, the temperature measuring device 10of the present invention is configured to introduce an inert gas intothe molten metal by and through the plug 22. Specifically, at its second22 b, the porous body 23 of the plug 22 is in contact with a source ofinert gas 35, preferably under pressure, by a gas inlet pipe 32. Inertgas is introduced into the body 23 of the plug 22 through the gas inletpipe 32. By its porous nature, the porous body 23 of the plug 22 isconfigured to inject inert gas into the molten metal from the first end22 a of the plug 22 via the pores. As used herein, the term “porousbody” includes any body having pores or channels that allow the passageof gas through the body from a gas source at the second end 22 b intothe molten metal at its first end 22 a. For example, the porous body maybe made of a naturally porous material or may be formed or drilled withsmall diameter gas pores or channels therein.

The metal housing 30 surrounding the plug 22 facilitates connection ofthe plug 22 to the inert gas source 35 by a connection between the metalhousing 30 and the gas inlet pipe 32 at the second end 22 b of the plug22. Accordingly, inert gas flows from the gas inlet pipe 32 into andthrough the pores of the porous plug body 23 from the second end 22 b ofthe plug 22 and is injected from the opposed first end 22 a of the plug22 into the molten metal. The connection between the metal housing 30and the inert gas source 35 is also useful for guiding and protectingthe connections of the thermocouple 28.

Preferably, the inert gas is nitrogen or argon. However, it will beunderstood by those skilled in the art that any gas of a sufficientlyinert nature may be used. The inert gas is injected into the moltenmetal by the plug 22 with sufficient pressure and density such that finebubbles of the inert gas are generated, but the injected inert gas doesnot cause an undesired outflow of the molten metal. The fine bubbles ofthe inert gas contact inclusions and micro-inclusions contained withinthe molten metal and, upon contact, the bubbles cause the inclusions andmicro-inclusions in the molten metal to rise relatively quickly andmigrate to the surface of the molten metal.

The bubbles of the injected inert gas also cause movement of the moltenmetal at and about the first end 22 a of the plug 22. More particularly,the injected inert gas creates a vortex of molten metal about thesensing portion 44 of the device 10, and particularly about thethermocouple 28, creating homogenization of the molten metal temperaturein the region of the sensing portion 44. Accordingly, the bubbles createa thermal equilibrium between the molten metal and the sensing portion44, and specifically the thermocouple 28, thereby leading to moreaccurate temperature measurements. Specifically, because the sensingportion 44, including the thermocouple 28, is in close or direct contactwith the molten metal in the recessed portion 40, homogenization of thetemperature of the molten metal is achieved and the temperaturemeasuring device 10 very quickly reaches its equilibrium temperaturewith the molten metal, so that measurement of the temperature of themolten metal may be performed very quickly and efficiently. The injectedinert gas bubbles also contribute to the homogenization of the chemicalcomposition of the molten metal.

In order to enable a continuous temperature measurement even duringtransfer operations of the vessel 12, a wireless data receiver (notshown) that transmits a data signal to a measuring instrument (notshown) is preferably used in conjunction with the temperature measuringdevice 10.

In preparing the temperature measuring device 10, the outer protectivesheath 24 is isostatically pressed from a carbon-bonded material andthen is trussed into the metal housing 30 with a refractory material,such as refractory concrete. Specifically, the portion of the outerprotective sheath 24 having a straight cylindrical shape is securedwithin the cylindrical recess 46 of the first end 22 a of the plug 22 byrefractory concrete, such that the tapered closed end 24 a of the outerprotective sheath 24 extends away from the first end 22 a of the plug22. Then, the thermocouple 28 and the inner protective tube 26 areinserted into the interior of the outer protective sheath 24 via acorresponding opening 15 formed in the plug 22.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

1. A container for molten metal comprising an outlet for outflow of themolten metal from the container and a temperature measuring device fixedin a wall of the container, wherein the temperature measuring devicecomprises a plug fixed in a wall of the container and having a first endand an opposed second end, an outer protective sheath having a closedend, an inner protective tube having a closed end, the inner protectivetube being arranged within an interior of the outer protective sheath,and a thermocouple arranged within an interior of the inner protectivetube, wherein the plug comprises a substantially refractory material andthe outer protective sheath consists essentially of substantiallyrefractory metal oxide and graphite, the outer protective sheathextending away from the first end of the plug and projecting into arecessed portion of the wall of the container, the closed end of theouter protective sheath being arranged in the recessed portion; andwherein a junction of the thermocouple is proximate to the closed end ofthe inner protective tube.
 2. The container according to claim 1,wherein the container is lined with a refractory material, the recessedportion being formed in the refractory lining material and configured toreceive flowing molten metal.
 3. The container according to claim 1,wherein the metal oxide of the outer protective sheath comprisesaluminum oxide.
 4. The container according to claim 1, wherein the innerprotective tube comprises alumina.
 5. The container according to claim1, wherein the plug comprises a porous body which is at least partiallyencased in a metallic housing.
 6. The container according to claim 5,wherein the second end of the plug is in contact with a source of inertgas and the porous body of the plug is configured to inject the inertgas into the molten metal from the first end of the plug, the injectedinert gas causing movement of the molten metal at the first end of theplug.
 7. The container according to claim 1, wherein the refractorymaterial of the plug comprises one or more materials from the groupconsisting of alumina, magnesia and spinel.
 8. The container accordingto claim 7, wherein the spinel is a magnesia-alumina spinel.